DESCRIPTION: The overall goal of these studies is to investigate the mechanisms by which TNFalpha (TNFa) modulates the growth and differentiation of mammary epithelial cells (MEC). Dr. Ip has made the unique observation that TNFa stimulates the proliferation of normal rat MEC and induces extensive branching morphogenesis in vitro. Moreover, TNF either inhibits (through the p55 TNF receptor [TNFR]) or stimulates (through the p75 TNFR) functional differentiation. These effects of TNFa appear to be physiologically significant, since TNFa and the TNF receptors are regulated during normal mammary gland development. The following studies are proposed in order to gain an increased understanding of the mechanisms by which TNFa exerts these effects, with the overall objective of determining the role that TNFa may play in the development of breast cancer. The first specific aim is to elucidate the pathways through which TNFa stimulates proliferation of MEC, with initial emphasis on the erk1/erk2, JNK and p38 MAP kinase pathways, and the accessory role of the EGF receptor. The second is to test the hypothesis that TNFa is a physiological regulator of mammary gland branching morphogenesis in vivo, with emphasis on altered expression of MMP-9 and stromelysin-1 as possible mechanisms by which TNFa stimulates invasion of MEC into mammary fat pad. The third specific aim is to determine the mechanism by which TNFa modulates functional differentiation, with emphasis on the putative effect of this cytokine on transcription factors known to regulate whey acidic protein and beta-casein transcription. And finally, to examine the effects of TNFa on NMU-induced rat mammary tumors, when administered locally by Elvax implant within the mammary fat pad. These studies will test the hypothesis that the activity of TNFa changes as cells become transformed.